(1) Field of the Invention
The present invention relates to a semiconductor device of the type sealed with resin and a method for manufacturing the same.
(2) Description of the Prior Art
In semiconductor memory devices having large capacities, "soft error" caused by radiation rays, in particular, alpha rays, has recently become a problem. This problem will become more serious with the increase in the degree of integration in semiconductor devices.
A variety of measures have been taken to cope with the problem caused by alpha rays, for example, designing the circuit so that the semiconductor chip itself exhibits resistance against alpha rays, protecting the surface of the semiconductor chip by a resin film, and reducing an amount of an alpha ray source contained in a sealing material. These measures, however, are not sufficiently effective. More effective measures have therefore been studied.
In a resin-sealed type semiconductor device, e.g., a resin-molded type semiconductor memory device, a semiconductor memory chip is sealed in a resin molded directly thereon, as is widely known. Fillers in the sealing resin contain alpha ray sources in large amounts. Therefore, as the integration degree of the device increases and memory cells are formed more finely, the problem of soft error becomes more serious.
In a conventional resin-sealed type semiconductor memory device, it has been attempted to apply a layer of resin without an alpha ray source onto the semi-conductor chip so as to block alpha rays. However, the resin layer applied has been too thin to achieve a sufficient shielding effect.
Moreover, in a conventional resin-sealed type semiconductor device, there is an additional problem that, according to the conventional method for manufacturing, the device, after the step of molding the sealing resin, chip-stage bars of a lead frame are cut in the vicinity of the side surfaces of the sealing resin. Therefore, the ends of the chip-stage bars are exposed at the side surfaces of the sealing resin. Also, the cutting force and resultant mechanical impact create clearances between the chip-stage bars and the sealing resin. Moisture infiltrates into the chip surface through the clearances between the chip-stage bars and the sealing resin, thereby affecting the reliability of the device.